1. Field of the Invention
The present invention relates to a telescopic cover for use as a movable cover of a machine tool.
2. Description of the Related Art
In a machine tool, a drive unit must be protected from chips and cutting fluids and a cover is used for this purpose. To prevent the machine tool from becoming bulky due to the presence of the cover, moreover, a so-called telescopic cover configured to extend and contract as a feed shaft axially moves is used as the protective cover for the drive unit. One such telescopic cover of a conventional machine tool will be described below with reference to FIGS. 8 and 9.
FIG. 8 shows a state in which a mobile element 1 is located at one end (right-hand end) of a fixed portion 12 in its movement direction (left-right direction in FIG. 8), and FIG. 9 shows a state in which the mobile element 1 is located at the other end (left-hand end) of the fixed portion 12 in the movement direction.
First and second fixed covers 2 and 3 are secured to the mobile element 1. These covers 2 and 3 support first and second movable covers 4 and 5, respectively, so as to embrace them. In this way, the first fixed and movable covers 2 and 4 form one telescopic cover, and the second fixed and movable covers 3 and 5 form another. Thus, the first movable cover 4 is movable relative to the first fixed cover 2 in such a manner that at least part of it is surrounded by the first fixed cover 2, while the second movable cover 5 is movable relative to the second fixed cover 3 in such a manner that at least part of it is surrounded by the second fixed cover 3.
Stoppers 20 and 21 are secured to the first and second movable covers 4 and 5, respectively. Further, stoppers 22 and 23 are secured to one and the other ends, respectively, of the fixed portion 12. When the mobile element 1, which is movable relative to the fixed portion 12 in the left-right direction, is located at the right-hand end, as shown in FIG. 8, the motions of the first movable cover 4 and the second fixed cover 3 are braked by the stoppers 22 and 21, respectively. When the mobile element 1 is located at the left-hand end, as shown in FIG. 9, in contrast, the motions of the second movable cover 5 and the first fixed cover 2 are braked by the stoppers 23 and 20, respectively.
Japanese Patent Applications Laid-Open Nos. 2011-025324 and 2007-276044 discloses a pantograph used to extend and contract a telescopic cover of the type described above. The pantograph is extended and contracted in synchronism with a movement of a machine by a feed shaft. However, this technique configured to extend and contract the telescopic cover by means of the pantograph has problems that the structure is complicated and expensive and that a link shaft is worn and broken by rapid axial movement.
On the other hand, Japanese Patent Application Laid-Open No. 8-57741 discloses a telescopic cover of the above-described type, comprising a first cover member and a second cover member supported by the first cover member. The first cover member is attached to a mobile element of a machine tool capable of reciprocating in a linear direction and movable together with the mobile element. The second cover member is movable in the linear direction in association with the action of the first cover member. This telescopic cover has a simpler construction than a telescopic cover which uses the pantograph or the like. In this structure, however, stoppers are arranged individually on the opposite side end portions of a movable range of the second cover member so that extension and contraction of the telescopic cover (i.e., first and second cover members) are suppressed by them. It is necessary, therefore, to follow rapid axial movement, thereby mitigating impact caused by the axial movement. Consequently, this telescopic cover is easy to break and requires scheduled maintenance.